Evidence suggests the variant of coronavirus that emerged in the UK may be more deadly, Prime Minister Boris Johnson said.

The data has been assessed by scientists on the New and Emerging Respiratory Virus Threats Advisory Group, which has briefed government.

However, all the evidence remains at a preliminary stage, he stressed during this evening's press conference. 

Studies have already shown it can spread more easily than other version of the virus.

The new variant was first detected in Kent in September. It has since become the dominant version of the virus in England and Northern Ireland and has spread to more than 50 other countries.

Mr Johnson said: "In addition to spreading more quickly it also now appears that there is some evidence that the new variant, the variant that was first identified in London and the south east, may be associated with a higher degree of mortality.

"It's largely the impact of this new variant that means the NHS is under such intense pressure."

According to England's chief scientific officer Patrick Vallance, 13 or 14 people per 1000 would die of the new strain, compared to around 10 of the old strain.

He said the coronavirus variant which emerged in Kent is “a common variant comprising a significant number of cases” and transmits up to 70% more easily than the original virus.

He told a Downing Street press conference: “We think it transmits between 30% and 70% more easily than the old variant. We don’t yet understand why that is the case.

“It doesn’t have a difference in terms of age distribution … it can affect anybody at any age, similarly to the original virus.”

He added that among people who have tested positive for Covid-19, there is “evidence that there is an increased risk” of death for those who have the new variant compared with the old virus.

Sir Patrick cautioned, however, that this is based on evidence which is “not yet strong” and there is “no real evidence of an increase in mortality” among those hospitalised by the variant.

“These data are currently uncertain and we don’t have a very good estimate of the precise nature or indeed whether it is an overall increase, but it looks like it is,” he added.